In recent years, household electric appliances and audio-visual apparatuses have been connected to a network, and various types of history information (what is called lifelog information, such as a user's use history of an electric appliance or television viewing history) are collected therefrom into the cloud. This creates an expectation that services utilizing the lifelog information collected in the cloud are provided. For example, there has been an expectation that such lifelog information collected in the cloud is utilized for provision of services in cooperation with a service provider, such as a personalized service appropriate for a life style of each user or a market analysis service wherein statistical information is used.
However, since the lifelog information involves privacy of each user, personal information included in the lifelog information should not be provided to third parties without permission from the user.
In view of this, there is proposed a method in which a service provider provides users with a service with security for anonymity of the users against the service provider (see Patent Literature (PTL) 1). In the method proposed in PTL 1, an online transaction service is provided to anonymous users.